For highly accurate temperature measurement that is stable over a long period of time, metal film resistors, in particular platinum film resistors, have been used due to the relatively strong temperature-dependence of the electric resistivity of platinum and its high chemical and physical resistance. The properties of platinum resistors for use in industrial temperature measurement are described in DIN IEC 751.
A common manufacturing method which is also used in large-scale industrial production is the vapor deposition of a metal layer, e.g., platinum, on ceramic substrates, which allows accurate control of the layer thickness and thus of the resistance for a given structure. The surface of this thin film can be subsequently shaped as desired by masking and etching. In order to obtain an absolute calibration and highly accurate resistance, the resistor structure must be trimmed. This trimming is performed using laser ablation, for example.
The above-described methods provide highly accurate temperature measuring resistors that are stable over a long period of time. The smallest surface resistor shapes and structures can be realized using manufacturing processes similar to those in the semiconductor industry. Using this manufacturing method, the shape of the metal film resistor on the surface of the substrate is relatively freely selectable. In order to arrive at the smallest possible shapes for a given desired resistance, and to enable the use of simple trimming algorithms, the resistors are usually given a wave-shaped structure.
Electrical contacting of the thin-film resistors is effected via contact wires soldered, bonded, or welded to the contact surfaces.
For temperature regulation, the combination of a temperature measuring resistor with a control element is needed. This control element may be a Peltier element or, for an application requiring long-term stability, a resistance heating element, for example.